1. Field of the Invention
The present invention relates to methods and materials for splicing or otherwise joining together carbonaceous materials, and more particularly to methods and apparatus for splicing carbonized polyacrylonitrile tows.
2. History of the Prior Art
During the manufacture of carbon fibers from polyacrylonitrile (PAN) precursor material, it is frequently necessary or desirable that tows of the polyacrylonitrile precursor material which have been oxidized and then carbonized be spliced or otherwise joined together. Splicing may be necessary, for example, where a plurality of the carbonized tows are simultaneously handled such as by winding on creels or bobbins. If one or more of the tows are shorter in length than the others, then splicing of the shorter lengths of tow to other lengths of tow becomes necessary so as not to interrupt the simultaneous winding or other processing of the tows. Splicing of carbonized tows may also be necessary where a continuous length of tow of specified length or poundage is to be provided. In such instances the processed length of tow may be too short so that one or more additional lengths of tow must be spliced thereto.
Carbonized PAN tows have a relatively hard composition and are of limited flexibility. Consequently, it is very difficult to join together two lengths of such tows by knotting or tying. However, even if knotting or tying were otherwise feasible, the equipment used to handle and process the tows typically advances the tows through eyelets and around sharp turns so as to prevent the use of tying or knotting.
In some instances carbonized PAN tows have been spliced together using an adhesive such as dissolved plexiglass. Such adhesives have been found to provide a splice which is relatively bulky and which in any event is too stiff to permit the tows and included splice to easily negotiate the sharp turns and eyelets within the processing equipment.
A satisfactory splice of two tows of carbonized PAN must be relatively strong and at the same time sufficiently flexible and compact so that the splice may readily negotiate the eyelets, sharp turns and other obstacles present in the equipment used to process such tows. These objects must be accomplished in the face of the carbonized tows which are themselves relatively stiff and inflexible and have relatively hard and smooth surfaces so as to resist adhesive penetration and bonding.